considered in Relation to the Phyllode Theory. 303 
Cypella , Dierama , Diplarrkena , Freesia , Geissorhiza , Gladiolus , Hesperantka , 
TrA, Ixia, Lapeyrousia , Liber tia, Marie a, Melasphaenda , Micranthus , Moraea 
(Dietes), P ater sonia, Schizostylis, Sisyrinchium , Sparaxis, Synnotia , Tapeinia , 
Tritonia , Wat sonia, Witsenia. The prevalence of the ensiform leaf, indi- 
cated by the length of this list (which is not exhaustive), seems to justify 
us in opening our consideration of the Iridaceae with a renewed attempt 
to understand this foliar type, which has been the subject of much 
controversy. 
(ii) Views hitherto held on the nature of the ensiform leaf. 
The anomalous character of the equitant Iris leaf has long been 
recognized; in Lyte’s ‘ HerbalH of 1578 it is compared to ‘the blade of 
a two-edged swoorde \ It is one of the most familiar examples of the 
c monofacial ’ leaf as opposed to the more usual flattened dorsiventral 
type. According to Celakovsky, 1 Velenovsky, 2 and others, 3 the ensiform 
leaf arises through congenital concrescence. This view has been most 
thoroughly and consistently elaborated by Celakovsky, who follows out 
and accepts all the deductions that arise logically out of his theory. He 
holds that the bifacial leaf is universally primary, and that all monofacial 
leaves are produced by concrescence of the halves, to right and left of the 
midrib, which were originally free and flat. He even goes so far as to 
suppose that all petioles came originally into existence through congenital 
folding and fusion of the narrowed basal region of bifacial blades. 
Velenovsky, however, while accepting Celakovsky’s view for the ensiform 
leaf, and even for those species of Iris which have a ‘ radial ’ limb, refuses 
to apply it to such apparently similar monofacial leaves as those of Juncus 
communis , which he interprets as due to the thickening of an originally flat 
blade. Goebel, 4 on the other hand, takes a view entirely opposed to those 
of Celakovsky and Velenovsky. He declines altogether to accept the idea 
of congenital concrescence, but he gives no explicit statement of his opinion 
as to the morphological nature of the limb. He treats it as a new wing- 
like outgrowth from the original leaf primordium, and, as far as one can 
judge from the way in which he discusses it, he seems to regard it as an 
organ sui generis. 
(iii) The ensiform leaf as a petiolar structure , and the comparison 
with Acacia phyllodes. 
In my 1918 paper 5 I have put forward the view that the equitant leaf 
which characterizes the Irises belonging to the Sections Apogon , Pogoniris 
1 Celakovsky, L. J. (1903). 2 Velenovsky, J. (1907). 
3 Gray, Asa (1887),; Chodat, R., and Balicka-Iwanowska, G. (1892); Balicka-Iwanowska, G. 
(1892-3); &c. 
4 Goebel, K. (1905) and (1913). 
6 Arber, A. (1918) ; Candolle, A. P. de (1827), recognized the leaf of Iris as petiolar. 
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